WASHINGTON (AP) — Senate Republicans warning of the devastating impact from looming defense cuts will hit four presidential battleground states next week, ratcheting up the political pressure on President Barack Obama even though Congress endorsed the reductions.

Sens. John McCain, Lindsey Graham and Kelly Ayotte announced Thursday that they will hold a series of town hall meetings in Florida, North Carolina, Virginia and New Hampshire — states that are home to military installations and defense contracting jobs.

The three said in a statement that they will "sound the alarm about the profound negative consequences of these cuts to our national security and economy. These communities, which provide our troops the equipment and support they need to defend our country, will bear the brunt of the defense sequestration cuts."

Republicans have blamed Obama for the automatic, across-the-board reductions in projected defense spending, but Republicans as well as Democrats voted for the cuts as part of a $1.2 trillion deficit-cutting plan.

The Senate by voice vote Wednesday night approved a bill requiring the administration to detail how it would make the cuts. The bill, which had already been approved by the House, now goes to the president.

The law implements nearly $500 billion in cuts over 10 years as the nation emerges from wars in Iraq and Afghanistan. If Congress can't find a way to avert the automatic cuts, known as sequestration, defense and domestic programs would face another round of cuts of about $500 billion apiece beginning on Jan. 2.

The cuts were set in motion by the failure of the bipartisan congressional supercommittee last November to produce $1.2 trillion in spending cuts.

Lawmakers have called the reductions catastrophic for the military. Defense Secretary Leon Panetta issued a fresh warning of his own on Wednesday.

"I sure as hell hope that sequestration doesn't happen," Panetta told a joint House panel focused on veterans issues. "It would be, as I've said, time and time again, a disaster in terms of the Defense Department, as far as our budget is concerned and as far as our ability to respond to the threats that are out there."

Panetta said it would mean double the defense budget cuts and the 100,000 personnel cut.

In real terms, however, the base defense budget has nearly doubled over the last decade, from $297 billion in 2001 to $529 billion in 2011. That amount does not include the billions spent on the two wars. The Pentagon envisioned spending would increase to $700 billion in 2021.

If the automatic cuts kick in, next year's Pentagon budget would face a cut of about $55 billion in projected spending from a half-trillion-dollar budget.

Graham, who traveled through his state of South Carolina in May, warned that the automatic cuts would force more than 180,000 out of the Army, cast doubt on the future of Fort Jackson and mean the termination of the F-35 Joint Strike Fighter, which is supposed to be based at the Marine Corps Air Station in Beaufort and Shaw Air Force Base outside Sumter.

Since then, Graham, McCain and several Democrats have discussed a possible one-year alternative to the automatic cuts that would involve raising revenue through changes in the tax rates. That idea, however, hasn't won much support from Republicans resistant to raising taxes.

Graham said in an interview that to force the issue in Congress, it's necessary to "create pressure outside the body. ... I hope Democrats will do what we're doing on the non-defense side. If I were a Democrat worried about the NIH's budget — I'm worried about it myself — I'd be out there doing what we're doing."

But he made clear he is frustrated with Obama.

"I think he's been AWOL," Graham said. "Quite frankly, it's an abrogation of his commander-in-chief responsibility to go to the VFW and criticize us when you haven't done anything to solve the problem."

Obama said in his VFW speech on Monday. "There are a number of Republicans in Congress who don't want you to know that most of them voted for these cuts. ... Now they're trying to wriggle out of what they agreed to."

Graham said he hopes to attach any plan to a bill to keep the government operating.

On the House side, the top Democrats on the various committees sent a letter to Speaker John Boehner, R-Ohio, calling for bipartisan negotiations to replace the automatic cuts with a balanced deficit reduction plan.

"We are confident that we can identify revenue sources and prioritize investments in a bipartisan fashion to avoid the sequester while achieving our deficit reduction goals," the 21 Democrats wrote.